AC electric motor vector control requires computationally intensive algorithms; this coupled with closed loop control and precise Pulse Width Modulation (PWM) makes vector control a difficult proposition. It has been established that converted motor direct-axis current, id, and quadrature-axis current, iq, of the rotating reference frame must be precisely controlled to provide good dynamic control of the AC motors. When performing AC motor vector control, synchronization of the measured phase currents, ia, ib and ic, with respect to the measured machine electrical position 9 is extremely important. This accurate synchronization is required for optimal machine performance which includes efficiency/output power, as well as to allow for very high speed operation.
In many existing designs the input phase currents and position signals are filtered using analog circuitry, whose delay is subject to tolerances of analog components. In addition to the tolerances, existing analog filtering requires a large number of components, which increases cost and size while reducing overall system reliability. The properties of the filter are also fixed, which lends to different machines requiring different controllers, as well as non-optimal filters used at different machine operating points. This filtered current is usually then fed to a Digital Signal Processor (DSP) which then reads the current and position and performs the synchronization of the phase currents with respect to rotor position. The DSP synchronization accuracy is also limited by the sequential nature of machine code and bandwidth limitations of DSP during operation.
Digital circuitry control schemes are sometimes used for control of AC motors. Digital circuits have the advantage of simple circuitry, software control and flexibility in adaptation to various applications. While digital control circuitry is sometimes used to control AC drives, it, too has limitations. Generating precise PWM gating signals and current control loops require a high sampling, rate to achieve a wide bandwidth performance. The field-programmable gate array (FPGA) is a semiconductor device that can be programmed after manufacturing, and even after a product has been installed in the field—hence the name “field programmable”. A FPGA has been used to implement general processing functionality and/or regular AC motor control for permanent magnet (PM) AC motors. However, modern machine uses at high speeds call for more precise synchronization between machine electric position and sensed motor phase current than is currently achieved.